The present invention relates generally to electroporation systems, and more particularly to providing flexible and efficient high throughput electroporation systems.
Electroporation is a technique that involves the use of an electric field to impregnate living biological cells, liposomes, and vesicles with exogenous molecules. High-throughput electroporation allows a user to apply an electric field, i.e., to “shock,” multiple samples either simultaneously or automatically in sequence. With the heightened interest in siRNA experiments, research using cDNA libraries, and the desire to perform rapid electroporation optimization, high-throughput electroporation is needed and demanded by scientists.
Electroporation occurs within a narrow range of parameters, such as pulse voltage and pulse duration, which is exhibited by a narrow window between electrocution and little or no electroporation. For example, if a pulse with too long a duration or too high a field strength is used, the cells may be lysed (destroyed). If the duration or field strength of a pulse is too low, electroporation efficiency is lost. The efficiency of electroporation is dependent on the cells, biological parameters, voltage, time constant (or duration), waveshape, current, heating, arcs, and other parameters. These parameters may adversely effect certain high-throughput electroporation systems.
One manufacturer (BTX Instrument Division, Harvard Apparatus, Inc., Holliston, Mass., USA) offers a high-throughput electroporator, which is described in U.S. Patent Publication 2006/0115888 (and PCT Publication No. WO 2004/050866 A1), the contents of which are incorporated herein by reference. The plates described in the above-cited patent applications have rectangular wells that contain plated electrodes. There are 96 wells arranged into 12 columns with 8 wells per column.
All of the electrodes on one side of a bank (i.e., a column) of eight wells are connected in common to plated traces along each bank, and all electrodes of the other side of the wells in the same bank are likewise connected in common. The plated traces end in electrical contacts, resulting in one anode contact and one cathode contact for each column. The electroporation plate is lowered into a device called a plate handler to place the plate into position for use. The plate handler connects with the 24 electrical contacts of the 12 banks of wells and has switches that connect each of the 12 banks in sequence to an external electroporator. Electric pulses are then delivered in sequence.
Since most cells live best in normal saline, shocking is typically performed in cells suspended in normal saline or other high-conductivity buffers. Wells containing normal saline present a relatively low resistance, which limits the electric current provided by the above electroporator since it is configured to shock eight wells at once. For example, it also causes a low resistance load (about 6.25 ohms) for the electroporator. Because of the low resistance of eight parallel wells and the fact that the maximum capacitor available has a capacitance of about 3200 mfd, the maximum time constant is limited to about 20 msec.
Thus, the electroporator is limited to shocking all 8 wells of a bank (column) simultaneously, and each bank is shocked separately. As explained above, this rigid operation limits the pulse width for many samples. Additionally, it prevents even more rapid electroporation by limiting the number of samples to eight. Also if all 12 banks are shocked, it takes about ten minutes of time for many protocols.
Therefore, it is desirable to provide electroporation system having flexibility in providing electrical pulses to many numbers of samples, and is also desirable to provide a sequence of pulses more efficiently.